This invention relates to extrusion dies for manufacturing extrudable articles from materials such as ceramic batches, molten glass, plastics, molten metals, and similar materials, which have the property of being able to flow or plasticly deform during extrusion while being able to become sufficiently rigid immediately thereafter so as to maintain their structural integrity. More particularly, the present invention relates to an improved extrusion die which is possessed with greater precision and accuracy than that known to the prior art.
An extrusion die of the general type with which the present invention is useful is disclosed in U.S. Pat. No. 3,790,654 to R. D. Bagley. Disclosed therein is an extrusion die for making honeycomb structures. The extrusion die disclosed by Bagley includes a large plurality of feed passageways which communicate with a still larger plurality of discharge slots. While disclosed by Bagley to be a unitary structure, it is known to form extrusion dies of the type shown therein by the joinder of two separate parts. U.S. Pat. No. 4,118,456 to Blanding and Van Dewoestine discloses such a two part die. The first of these parts is a unitary structure known as a backplate or die which is perforated by a large plurality of the aforementioned feed passageways. The second part is also a unitary body which is provided with a larger plurality of discharge holes and a still larger plurality of discharge slots.
In accordance with the aforementioned Blanding et al patent, it is generally known to bond the first and second parts together, for example, by brazing.
As must be apparent to those skilled in the art, the precise alignment of discharge slots vis a vis their associated feed passageways is critical to the extrusion of a honeycomb structure having uniform sized openings therein. In the past, when brazing a faceplate having discharge slots to a backplate having feed passageways, thermal expansion and subsequent contraction during and after brazing has, at times, caused misalignment between the discharge slots and feed passageways in the resulting extrusion die. This has occurred even though alignment dowels have been employed between the backplate and the faceplate which are designed to prevent warping and skewing since the faceplate at times binds or catches on the dowels during cooling and contraction, thus causing misalignment and subsequent failure of the brazed joint during extrusion.
It is an object of the present invention to provide an improved extrusion die employing a separate backplate having a plurality of feed passageways and a faceplate having a larger plurality of feed holes communicating with a still larger plurality of discharge slots to be aligned therewith, which are joined by brazing but which does not suffer the disadvantage of misalignment associated with prior art extrusion dies.